rtc: da9063: convert header to SPDX

Covnert the header of the source file to SPDX.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>